Typically, as an imaging method related to a magnetic resonance imaging apparatus, the fast spin echo (FSE) method is known. The FSE method is an imaging method in which firstly a flip pulse is applied to a person being tested and then a plurality of flop pulses is sequentially applied the person being tested so as to collect a plurality of echo signals called an echo train. Herein, a flip pulse is a radio frequency (RF) pulse used for excitation of the nucleus spin inside the person being tested; and flop pulses are RF pulses used for refocusing the phase of the nucleus.
In this FSE method, since a plurality of RF pulses is applied, the generation of spin echoes is accompanied by the generation of stimulated echoes. Because of the stimulated echoes, sometimes phase shifts occur in the echo signals that are collected. Such phase shifts cause degradation in the image quality in the form of unevenness in the photographic sensitivity, signal deterioration, or ghost image formation.
In order to prevent such degradation in the image quality; generally, a main-scan is preceded by a pre-scan so as to measure the phase differences occurring in the echo signals. Based on the phase differences measured during the pre-scan, the pulse sequence for main-scanning is corrected. In that case, for example, during a pre-scan, a pulse sequence for cancelling the stimulated echoes is implemented and only the spin echoes are collected. Then, of the spin echoes collected during the pre-scan, the first echo signal and the second echo signal are subjected to Fourier conversion in the readout direction, and a zero-dimensional phase shift and a one-dimensional phase shift between the first echo signal and the second echo signal are calculated. Subsequently, based on the zero-dimensional phase shift and the one-dimensional phase shift, a correction amount is calculated for correcting the phase shifts in the readout direction and the slice selection direction, and the pulse sequence for main-scanning is modified according to the calculated correction amount.
However, in the technology described above, it is not possible to correct the phase shifts that occur in the phase encode direction due to the effect of the eddy currents generated by phase encode gradient magnetic fields. Such phase shifts sometimes cause degradation in the image quality.